1. Field of the Invention
The present invention relates to semiconductor microelectronics and light emitting technology and more particularly, to a high-brightness yellow-orange yellow phosphor for use in the fabrication of warm white LEDs, which is prepared from a rare earth element YAG (Y3Al5O12):Ce3+ based substrate added with Li+1, Mg+2 and N−3. Following increase of the concentration of Li+1, Mg+2 and N−3 in the composite of the phosphor, the strength of the maximum value of the phosphor spectrum is enhanced by 5˜13%.
2. Description of the Related Art
Because of low efficiency and strength during the first development stage, LEDs are simply used for analog and numerical signal indication. After issue of the fundamental paper from Japanese researcher S. Nakamura (refer to S. Nakamura and. Blue laser. Springer Verl. Berlin 1997), an ordered of quantum size architecture in In—Ga—N semiconductor heterojunction is established, resulting in enhancement of semiconductor architecture radiation strength over several tens of hundreds of times. Thus, light radiators-LEDs begin for home, building and landscape illumination. Thereafter, researchers of “Nichia Corporation” created white light LED in which the first blue photoluminescence excites yellow phosphor to produce yellow long wave photoluminescence. In conformity with Newton complementary color principle, the two radiations are combined into a light beam of bright white light. It is to be fairly pointed out that a long time before the aforesaid Japanese researchers, Russian engineer discovered Ga—N semiconductor heterostructure-based Stokes phosphor (the wavelength of the radiation light is greater than the wavelength of the excitation light) for use to produce any color radiation including white light. The invention used the prior art of the Japanese engineers as a standard. These prior art designs use the known rare earth elements to synthesize garnet substrate-based phosphor that uses cerium for activation, having the stoichiometric formula: (ΣLn)3Al5O12.
The rare earth elements used are Y, Gd, Ce and the periodical cycle system group IIIA elements used are Al and Ga. Changing the ratio of yttrium and gadolinium can control the radiation spectrum of the main activator in the phosphor material activated by Ce+3 and simultaneously shift the luminance maximum value to λ=538˜560 nm. Changing the ratio of Al+3 and Ga+3 in the anion crystal lattice of the compound causes the phosphor to change its photoluminescence-excitation spectrum. Increasing the content of gallium ion to substitute for aluminum ion can shift the maximum value of the photoluminescence-excitation spectrum to λ=465˜445 nm.
Many patent disclosures and samples made contribution to phosphor for warm white LED. For example, one inventor of the present invention, doctor Soshchin compared the grades of various different phosphors for white LED. However, the technical problem is complicated. At first: YAG-based conventional phosphors, i.e., (Y,Gd,Ce)3Al5O12-compound has no any continuous solid solution series in the all Y—Gd-concentration. Extreme value [Gd]≈0.35 atomic fraction has low thermal stability at this time and, when heated to T=100° C., the efficiency of quantum radiation dropped substantially by 50%. The other problem (please refer to Abramov. V. C. Russia N635813 Sep. 12, 1977) is that, the novel garnet material Mg3Ln2(Si,Ge)4O12:Ce has low efficiency despite of being capable of creating λ>600 nm orange yellow-red phosphor.